\begin{Schunk}
\begin{Sinput}
 print(a, digits = 20)
\end{Sinput}
\begin{Soutput}
[1] 57.499999999999992895
\end{Soutput}
\begin{Sinput}
 print(b, digits = 20)
\end{Sinput}
\begin{Soutput}
[1] 57.5
\end{Soutput}
\end{Schunk}
